Non-aqueous electrolyte batteries as typified by lithium ion secondary batteries have high energy density, and therefore they are used as power sources for various moving devices such as automobiles and motorbikes, portable personal digital assistant devices, uninterruptible power supply (UPS) apparatuses, and storage devices. For such applications, in order to further improve energy density, laminate type lithium ion secondary batteries in which a power generation element is sheathed with a flexible laminate sheet are often used. Furthermore, in order to obtain a desired battery capacity, battery stacks in which a plurality of laminar secondary batteries (battery cells) are stacked and connected in series are also in practical use (see, for example, Patent Document 1).
Such a battery stack in which a plurality of battery cells are stacked is housed in a case together with a circuit board to constitute a battery pack. The circuit board is provided with power lines for connecting the battery stack and external connection terminals, and a protection circuit. The protection circuit includes a current monitoring unit for monitoring the current of the power lines, a voltage monitoring unit for monitoring the voltage of the respective battery cells constituting the battery stack, and a control unit for outputting a signal for shutting off the power line when detecting an abnormality based on outputs from the current monitoring unit and the voltage monitoring unit. In conventional battery packs, the power lines and various functional components constituting the protection circuit are provided on one common board (see Patent Document 2).